Scientists have been voicing concerns about water shortages for several years now, and a recent UN report estimates that by 2025, two-thirds of the world’s population will face freshwater shortages.
When you consider the facts, it’s not hard to understand why there’s a looming problem. The world’s population tripled in the 20th century and is expected to increase by another 40-50% in the next 50 years. By the year 2050, 4 billion people (over half of the entire world’s population) will be facing severe water shortages.
By the year 2025, 2 out of 3 people will face freshwater shortages. A new desalination technology could help reduce the shortfall.
The water shortage has yet to significantly impact the United States, at least not on par with how other parts of the world are already struggling. According to the World Water Council, 1.1 billion people are currently living without clean drinking water.
Any breakthrough would not come a moment too soon. Many countries are eyeing the oceans as a potential source of drinking water. However, seawater must be desalinated in order to be a viable alternative, and today’s desalination plants have their own unquenchable thirst – for energy.
Energy is needed to drive reverse osmosis (RO), the process in which salty water is forced at high pressure through a membrane that lets water molecules through, but blocks the salt. The amount of energy required to run a desalination plant is formidable.
But now several researchers and startup companies think they have a more energy-efficient alternative and it works by turning RO desalination on its head.
RO is an inherently energy-intensive process. So instead of fighting this energy, why not try to harness it? That’s the thinking behind the experimental Forward Osmosis plants that are starting to appear. Water can be sucked effortlessly out of seawater if you offer it a more concentrated “draw solution” to flow into.
One of the first companies to harness the power of forward osmosis is Hydration Technology Innovation (HTI). The company released the X-pack, a portable water filter that incorporates a forward osmosis membrane into a small sealed plastic packet. Inside the packet is a powder containing sugar and flavorings, which act as a seed for the draw solution.
According to HTI, the packet can be thrown into a mud puddle and the powder will draw the water molecules through the membrane to create a drink. Many US soldiers now carry these packs, which can be thrown over the side of a boat to pull a sweet drink out of the sea.
But the X-pack is not going to solve the world’s water crisis. A research team at Yale University hit on an idea that took the concept a step forward. The researchers decided to use a draw solution based on ammonium bicarbonate. Just as HTI’s sugary powder does, the ammonium and bicarbonate ions can pull water through the membrane. If you then heat the solution to around 40°C, ammonia and carbon dioxide are given off, leaving behind pure water. The team says its low-grade heat method could produce fresh water while using substantially less energy of today’s desalination plants. Their technology is being marketed by the company Oasys who hopes to have a small plant built by mid-2011.
Using forward osmosis rather than reverse osmosis greatly reduces the energy requirement compared to a RO desalination plant (shown above)
A team of researchers at the Singapore Membrane Technology Centre has developed a membrane consisting of tiny tubular fibers that can be used with ammonium bicarbonate as the draw solution. Salt water passes down the center of the fibers while the draw solution swirls around the outside. Wang Rong, deputy director of the Center, states this type of membrane has the potential to reduce the energy used for seawater desalination by 30%.
Meanwhile, the company Modern Water is successfully deploying forward osmosis using 30% less energy than conventional desalination. Instead of ammonium bicarbonate, Modern Water uses a proprietary salt to suck the water through their membrane. Modern Water says their technology is already in use at a pilot plant in Gibraltar and at a full-scale plant in Oman.
Forward osmosis uses low levels of energy to yield high levels of clean, healthy water.
So, is forward osmosis the answer to our water needs? There are hurdles to overcome according to Mark Shannon, Research Director of Desalination Materials at the University of Illinois, Urbana-Champaign. He is concerned that the cost of the membranes may be prohibitive. “The water flux in forward osmosis is low, so a lot of membrane is required,” he says.
However, Shannon sees great potential for forward osmosis in recycling waste water. And, the technology may turn out to be ideal for desalinating brackish water, such as deep underground water and estuary water. Deep underground water is plentiful.
“Underlying almost every continent are large sources of brackish water,“ Shannon says. “Forward osmosis could be a smashing success.”
Photos: Jose Luis Roca; Peter MacDiarmid / Getty Images
Source: New Scientist